Lower frame midrails in an automotive vehicle support the central part of an automotive chassis and provide a cantilevered support for the rear bumper assembly. Conventionally, the rear bumper assembly would include a transverse bumper beam, lower frame rails and appropriate attachment brackets for connecting the bumper beam to the lower frame rails and the lower frame rails to the midrails. The rear shock tower support members are mounted on top of the midrails, conventionally in a cantilevered manner off of a single fabricated rail structure.
The structure of a lower frame midrail can vary significantly from manufacturer to manufacturer. As can be seen in U.S. Patent Publication No. 2004/0080188, filed by Masanori Igarashi, et al and published on Apr. 29, 2004, the longitudinal frame rails are connected by a cross frame member with legs that straddle the shock absorber column. A bracket is placed over the leg to mount and support the shock absorber. In U.S. Pat. No. 4,708,391, issued to Mitusou Nakano on Nov. 24, 1987, the longitudinal frame rails are reinforced by a member that is located adjacent both longitudinal sides of the shock absorber spring.
U.S. Pat. No. 5,411,311, issued to Roger Shimmell, et al on May 2, 1995, and assigned to Ford Motor Company, the front shock absorber towers are braced with a transverse member between the towers and members located between the cowl and the shock absorber towers. U.S. Pat. No. 5,988,734, issued to Stephen Longo, et al on Nov. 23, 1999, teaches a conventional bumper mounting configuration wherein the vehicle frame is reinforced by a central tunnel and reinforcing pads between the tunnel and the rails. Akira Nomura, in U.S. Pat. No. 6,773,057, issued on Aug. 10, 2004, teaches that the front shock strut tower can be supported on an apron, which is reinforced by members that extend between the longitudinally extending tubular members.
It would be desirable to provide lower frame midrails for use in conjunction with a bumper and lower frame rail structure of an automobile that are particularly adaptable to manufacturing through hydroforming processes and which can be utilized to provide a stable support for the rear shock tower.